The ultimate goal of this project is to establish how the alfalfa symbiont Rhizobium meliloti crosses the plant cell walls during establishment of nitrogen fixing nodules. Results of others suggest this involves degradation of cell wall polysaccharides (cellulose, hemicelluloses and pectic substances). Preliminary results have identified an activity that releases reducing sugars from polysaccharides as well as an activity (probably different from the preceding one) that degrades polysaccharide in an agar plate test. In addition, DNA sequences may have been identified that hybridize with a cloned pectate lyase gene from Erwinia chrysanthemic. These results will be pursued to characterize the genes and gene products involved. This should elucidate the mechanism of rhizobial invasion of legume roots, which in turn should provide valuable information for genetic engineering of nitrogen fixation, with corresponding benefits to human health and nutrition.